In the fusion reaction of deuteron and triton, alpha particles are more than a mere by-product. Their kinetic energy of 3.5 MeV is actually transferred to the plasma, which has the effect of heating it up. One challenge in realizing a fusion reactor involves determining how the alpha particles can be better confined and the self-heating sustained.
Kunihiro Ogawa and colleagues studied the confinement of triton produced in deuterium plasma operations in the Large Helical Device because it exhibits behaviour similar to the alpha particles created in deuteron–triton reactions. With newly installed neutron diagnostics, the ratio between the neutron emission rates from a deuteron–triton and deuteron–deuteron reaction was measured for different magnetic-field configurations. When the magnetic-field axis was shifted inwards, this burn-up ratio increased significantly and revealed better ion confinement. The maximum value of the burn-up ratio was comparable to those obtained in middle-sized tokamaks such as KSTAR and promises good confinement of alpha particles in helical devices.